As illustrated in FIG. 4, the control device of this type typically includes a base unit 9 incorporated with a plurality of slots 1, 3, 5, 7, . . . which are mutually connected by a composite signal line (which is not shown in FIG. 4), and the user may install a plurality of input/output units (controlled units) 15, 17, . . . as well as a power unit 11 and a CPU unit 13 serving as a main control unit into the slots 1.about.7, . . . . In the drawing, numerals 19a.about.19d denote connecting terminals provided in the slots 1.about.7, . . . for electric connection with the corresponding units 11 .about.17, . . . .
In this control device, with electric power from the power source unit 11 supplied to the other units 15.about.17, . . . , the CPU unit 13 controls the individual input/output units 15, 17, . . . by designating addresses. For instance, according to temperature values obtained from the input/output units 15, 17, . . . the CPU unit 13 determines a certain procedure and computes control values, and forwards such data to the object to be controlled (not shown in the drawings) to control the temperature of the object to be controlled according to a fixed set point control mode or a programmed control mode.
According to such a control device, typically, the slots 1.about.7, . . . are provided in the base unit 9 by a number greater than normally needed so that the user may add or remove the input/output units 15.about.17, . . . having different functions according to each particular need.
Therefore, it is necessary to allocate unique addresses to the input/output units 15, 17 . . . when or before they are installed into the individual slots 5, 7 . . . for the CPU unit 13 to be able to accurately control the input/output units 15, 17 . . . by specifying them by their addresses.
Conventionally, address allocation terminals and dip switches (which are both not shown in the drawing) were provided in the circuit board or the like of each input/output unit 15, 17, . . . and the terminals were connected by jumper wires or the dip switches were manually operated according to the type of each particular input/output unit 15, 17 . . . . Thus, different addresses were manually allocated to different input/output units by the user so as to avoid any repetilions in the address allocation and not to cause any confusion as to the types and the functions of the units. For instance, "1".about."5" may be allocated to digital input/output units, and "6".about."9" may be allocated to analog input/output units.
However, allocating addresses to different input/output units 15, 17, . . . by using jumper wires and dip switches involves a highly laborious work for the user, and address allocation may not be correctly carried out, thereby resulting in the failure of the control device to operate properly.
Some of the recently developed small control devices allow a desired number of independent base components each incorporated with a slot to be installed on rails or the like so that the user can install input/output units into any of these base components according to his need. In regard to such an arrangement also, it has been desired to be able to allocate addresses to the input/output units without altering the hardware of the base unit for the convenience of both fabrication and handling.
It thus has been desired to provide a control device which uses independent base components and does away with the arrangement for address allocation so as to reduce the effort required by the user. The inventors have therefore directed their attentions to the individual base components for connecting various input/output units, and have developed a control device which can reduce the effort required by the user for setting up addresses.